Regulation of transcription in expressed and unexpressed mating type cassettes of yeast

Abstract
The genes that control the a, .alpha. and a/.alpha. cell types in Saccharomyces are carried on transposable elements known as a and .alpha. cassettes which reside at 3 different chromosomal loci. Examination of the transcripts by R-looping and filter hybridization indicates that each cassette is capable of producing 2 divergent transcripts. Cassettes at the MAT locus are transcribed constitutively. Transcription of cassettes at HML and HMR is prevented by trans-acting negative regulators.